When the solenoids of certain solenoid valves are operated from de-energized to energized, a metal pin, or plunger, that is disposed in a flow path through the valve is operated from an original position to unseat a spring-biased valve element, and thus open the flow path. When the solenoid is de-energized, the spring re-seats the valve element, thereby closing the flow path, and causing the pin to be returned to its original position.
An example of such a solenoid valve is one that is used in a hydraulic adaptive braking system of an automotive vehicle. Due to its proximity to the solenoid valve's magnetic circuit, the metal pin had to be made from non-magnetic stainless steel. To assure adequate life for the pin, it was necessary for the tip end to be hardened by iron nitriding. Since the pin was disposed in the fluid flow path, it had to provide for the fluid to flow past it, and thus required machining to provide axial flow channels to carry the fluid flow. The use of such material and such procedures contributed to the cost of the pin.
The present invention relates to a new and improved construction for such a pin. As a result, the pin of the invention can be manufactured from less costly materials using less expensive procedures. Specifically, the pin comprises a comparatively slender, generally cylindrical metal core that is surrounded by a plastic sleeve. The nature of the core allows for it to made from a material, such as 52100 steel, that can be thoroughly hardened, a less expensive and more reliable process than the limited hardening conducted on the prior pin, and such a slender core will not exert any significant detrimental influence on the magnetic circuit. The core does not require the elaborate machining procedures that characterized the prior non-magnetic stainless steel pin. The plastic sleeve is simply overmolded onto the metal core by an injection molding process. The sleeve defines axial channels that allow fluid to pass along the pin. The sleeve has a composition that is both inert to hydraulic brake fluid and will present a suitable surface characteristic to the wall of the fluid path in the valve body within which it is closely guided for axial reciprocation as the solenoid is energized and de-energized, and the axial channels that are defined by the sleeve serve to promote better flow of fluid past the pin.
Further features, advantages, and benefits of the invention, along with those already mentioned, will be seen in the ensuing description and claims which are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.